hi! does anyone have any idea how to fix the power switch on a game boy advance?

my partner bought a customized one years ago (with a built in back light) but it doesn't reliably turn on and occasionally turns off unexpectedly... the folks he bought it from have been unresponsive, and he's convinced the people i interact with are more likely to have this knowledge than anyone he'd know ("they seem like nerds")....

i don't expect this is enough information to go off of, but any resources for figuring this out would be helpful too (or if you happen to do or know someone who could repair this he'd probably prefer to send it out than let me play with it hahaha - he'd of course be willing to pay if that was the case)