How can I make DIY refills for home fragrance bottles?

never heard about that but will love to find out myself

I'm assuming you're talking about the wall flowers, correct? If so, here's a tutorial: https://www.youtube.com/watch?v=S9-52sGzaMc

I'd love to find out how to do this!

https://www.hometalk.com/diy/clean/how-to-reuse-bath-and-body-works-wallflower-bulbs-read-more-at-http--19523717

https://www.hometalk.com/diy/decorate/rooms/homemade-oil-plug-in-refill-6975850

https://www.hometalk.com/diy/diy-air-freshener-717571

Hometalk Projects might be the answer.

Hi Heber: Transferring fragrance into a bottle, you can use a funnel or syringe. For refillable bottles, simply unscrew the atomizer, pour in the new scent, and tighten. For atomizers, pump the base onto the nozzle. If you still have the old bottle, you can just pour some perfume into the jar. You can get perfume or room freshener from the dollar store pretty cheaply.

Hello Heber, hope this helps you. Refill empty Bath & Body Works Wallflower bulbs by popping off the plastic cap/wick assembly with a needle-nose plier or flathead screwdriver. Clean the bottle, then fill with a mix of roughly 75% fragrance oil/diffuser oil and 25% water or carrier oil, or use essential oils. Reinsert the wick/cap, snapping it back into place, and plug in.