Personally I would not reinstall, but the welcome app not working is perhaps a sign of deeper problems, but I’m not sure what you mean by “not working”.
There’s a wonderful wiki article [1] about system maintenance, amongst which how to update mirrors through cli.
reflector --protocol https --verbose --latest 25 --sort rate --save /etc/pacman.d/mirrorlist
[1] A Complete Idiot's Guide To Endeavour OS Maintenance / Update / Upgrade