Is there a way to preserve a dying bonsai tree

It's a regular tree that's been trained to grow this way so what kills regular trees? Maybe to much water for the container and you have root rot or maybe not enough? Maybe it's suffered some stress have you moved it from a previous location? How about insects? Too much pruning or just not at the right time. I would approach it as if it were a tree outside. Does it receive enough light for the type of tree it is?

Depends on the type of tree. Pine needs to be outside and if inside, needs humidity so as not to dry out. Is it deciduous? Does it have leaves and is losing them?

for the correct answer....http://www.bonsaitreegardener.net/how-to/brown-leaves

First step is to identify the type of bonsai tree you have, and then figure out the specific care it requires. This article should help you out-https://www.bonsaiempire.com/blog/revive-dying-bonsai

If you are over watering this may cause your tree to drown and die off. Cut back on the water for a while until the soil is dry and then water thoroughly again, let drain and then let it dry out again until the next watering.