Place the solder at key points. Be careful - the parts have to fit tightly to each other. Otherwise the solder will not be able to connect them.
Heat to flow the solder. Prepare other places for soldering by cleaning off the fire scale with a file.
Place three pieces of solder and heat to flow the solder. Be careful, you don't melt the copper, only heat to the desired temperature. Otherwise, the solder will change its color to silver.