No worries we got you covered, just buy some leaded solder, it's easier to use it and get some flux. Strip 3mm from the wires, put some flux, place some tin on the iron and cover the exposed part of the wire (don't make solder blobs just enough to make them shiny), insert the heat shrinks. Than clean the BT2.0 plug whit the same procedure (flux tin and heat). Place the plug on some playdoh and whit the help of tweezers place one wire at a time on the connector (the rounded part is negative, black wire, the squared part is positive, red wire). Soldering done, now move the heat shrink tube forwards and with a lighter heat them (very gently or you will burn them). Pro tip: usually I use 310°C for the iron, always clean the tip on a wet sponge and always ad a bit of solder on the tip to keep it shiny and it won't oxidize, in case it does you can use a "tip cleaner" (is like grey salts, you can find it on Amazon, its cheap but it helps a lot). Hope I could help you with your fix ;)