Decrypt password created with htpasswd
.htpasswd entries are HASHES. They are not encrypted passwords. Hashes are designed not to be decryptable. Hence there is no way (unless you bruteforce for a loooong time) to get the password from the .htpasswd file.
What you need to do is apply the same hash algorithm to the password provided to you and compare it to the hash in the .htpasswd file. If the user and hash are the same then you're a go.
See in particular Apache HTTPd Password Formats