iphone6 unavailable

Unfortunately, no. The only way to unlock it is to do a reset, it will wipe all data off the phone. Hopefully he made backups.

If you forgot the passcode on your iPhone, or your iPhone is disabled or unavailable -

Click on the link for instructions on how to reset your passcode without a computer if you have iOS 15.2 or higher.

If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

Click on the link for instructions on how to reset your passcode using a computer.

If you forgot your iPhone passcode - Apple Support

That depends, if it says something like try again in 8 hours, then yes, he may have another chance. If it just says unavailable, then no, it won't ask you again.