To allow microphone in a site , either you blocked it
 before or not, you should go to the permissions of this site ..

 ↓ click to see full image ↓
At first , you should go to the wanted site .


click the small lock icon beside the URL .

Then you should click " site settings "
Change the permission for the microphone from ask or blocked to allow.

you can use this method for any permission in any site even on mobile browser.