Are they the kind that have two parts with the middle part popping up? This kind uses the middle part to lock the outside in place and you have to pull the inside up first before you take them out. I’d also recommend buying a tool to remove them like this https://www.amazon.com/XBRN-Removal-Window-Fastener-Remover/dp/B08GKK5ZTL
If there’s already some old solder where you have to solder again, add a little new solder it before removing the old. Make sure that the pad is clean before you solder your new piece in place. Heat up the metal and touch the solder to it, don’t try just heating up the solder and letting it drip on.
I don’t know what you mean by “siringe instead of fat” though.
[email protected] I think is how you do it.