Any way to repair this myself? moisture coming from the toilet .

You will need some plumbing skills to pull that off.

removing flooring and exposing sewar drain. And tying into existing drain

the finishing tile is the easy part

Yes you can. You will need to remove all loose material and the grout along the blue tiles. Use a stiff trowel or putty knife to knock down the ridges in the thinset on the left of the photo. Fill the hole with cement mix (not concrete mix) forcing it under any voids and smoothing it level with the floor not the blue tile. Cement mix has no gravel in it while concrete mix has gravel in it. Dampen the old concrete for the new to bond to the old. Once it's dry and hard you can lay your tile with thinset and grout the seams. I hope you solved the leak from the toilet by replacing the wax ring. That's probably where the moisture came from.

Looks like there is a problem under the tile that needs to be fixed. At least call a plumber to get a quote and to find out what exactly the problem is.

That much moisture I really doubt is from the toilet sweating. You need to locate and fix the leak first.

Have you noticed any poo colored stains around the bottom on the toilet where it meets the flooring?

You should also use a bonding agent on the old concrete before applying the new mix. Another choice is a sand bedding /topping mix, which also has no gravel.

William (as usual) has provided great advice. The wax ring is replacement is one of the most important steps.

You can hire a handyman that knows how to set tile. You can find one locally using ANGI or Thumtack websites. Try to get at least three quotes, photos of jobs they've done, past clients you can get in touch with.

First, you will need to fix the problem that caused the leak. After that, remove any loose mortar, etc and fill in the area with cement. Skim it so it's level and when dry, you can lay new tile.

It is going to be a difficult job for you if you do not have plumbing skills. I would check on Nextdoor for recommendations. I just hired someone from one of the above sites and It was a total disaster.

I see you said the original issues is fixed. You should be able to chisel up the area beneath the tiles that were damage. It looks like the sub flooring is also in need of repair but you should be able to do that with mortar mix, I believe William covered that part. Make sure you have clean lines on your grout against the remaining tiles. It is most likely you will need to replace the cement board beneath them. Then use thinset and a notched trowel to put down a layer, then set your tile. I would recommend picking up some tile spacers unless you are really good at spacing. Once the thinset is dry, grout and seal the area. When you put in the toilet, make sure to use a new wax ring set. We tried the rubber replacement on one that had cracked and found that it doesn't work well with an older pipe so we ended up going back to the wax ring.

Cement the hole closed,then add tile sghesive down then place tiles in place then when dry grout

it seams there is issue under tiles .. You need to take care of that

Oh dear, that’s a can of worms, so sorry. Truthfully, the best and right way to repair it is take out all the tile, repair the drain damage, then put in new tile. You can do some patching and stick in more of the blue but if what’s under the toilet is causing this to happen, it’s only going to happen again and be more costly to repair.

The best thing that you should do first is to find the cause of the problem, Then, you can remove any loose mortar, etc. and just use cement to fill in the area. I also suggest you skim it so it's level and when dry, you can lay new tile.

Call in a Builder and ask for quote plus time it will take. Then decide!