Set Microphone input to Audio output

Solution 1:

You probably can't, unless the input is designed to be internally switchable [which would be very unusual on consumer equipment].

Both your input voltage & impedance will be badly mismatched.

Mic level is something like 1000 times less than line level, so even ignoring the impedance, you will be shooting your mic input with up to 1000x too much power. Even allowing for consumer 'line' level to actually be at -20dB rather than 0dB [because it's much, much cheaper to make] you still have a massive discrepancy.

I'd suggest buying an attenuator, but a) the plugs won't match for consumer audio & b) it would be cheaper to get the line socket fixed.

Here's a not too technical explanation, from Shure - Mic Level And Line Level -- What Do They Mean? though they are talking about pro equipment, the rules still pretty much apply to consumer gear.