How to tuning the FM reciever to be the high gain?

My FM reciever has sensitivity about -80 dBm But I need sensitivity at -100 dbm or more.
How can I tuning? Which part of circuit can be tuning? Please .......Thank you very much

A big antenna with lots of gain will overcome the receiver's limitations. But you would now have to point the antenna (physically) at the station.

You could buy a "powered" antenna. Terk makes one, as do others. The antenna has a built in low noise amplifier. When using this powered antenna (with ~22 dB of gain), the receiver sensitivity will become around -102 dBm.

I have just only one antenna(1 station) on my FM reciever (wireless microphone) but I want to use two frequency in my reciever (2 microphone). How can I do?

Sensitivity of your FM receiver is in "normal" range so you can use better antenna and/or antenna preamplifier.

Then you hav to make sure the antenna can cover the two freq.