Best tricks to remove iPhone 5C battery glue?

It would be difficult to remove it without touching the logic board, or at least removing some of the screws. The least you can do is to remove the charging port, so that you will have full access to the end of the glue (near the charging port. there is a piece there attached to the glue strip). Pull the black piece out, cut it in half, and pull the glue strip gently one side at a time (there are 2 glue strips at the bottom of the battery). hth.

Honestly, this battery can be difficult to remove if it something that will be reused after putting it back together, if not just be aware of where the logic board is, you want to be as careful as you can but Im sure you already knew that, make sure that the battery is disconnected from the logic board first, and since you are replacing the battery there is no need in being nice to it, if you have followed the steps in the guides on this site and they didn't help then i would suggest getting some kind of flat tool like a spudger or a flat head screw driver and very carefully pry it out while avoiding the logic board, just work your way around until it comes free, *This is just my opinion on what I would do with MY phone, some might not condone it here but again this is just MY opinion*, hope i helped