If the hacker sees your VPN subscription details (username and password) he might have all the information you have. Unless access to the VPN is protected by an additional factor the hacker does not have or know, the hacker can then use you VPN credentials too.
Such additional factors might by physical or software based multi-factor authentication. It might also be that you get an email (where the attacker has no access to) if a new device was added and that you explicitly need to enable the device. If a VPN provider offers or requires the use of additional factors though is specific for the VPN provider.
Can the person with access to the compromised device find the ip the vpn has given my other device?
It might be that the VPN provider offers such details for anybody who knows the correct credentials. If this is the case again depends on the specific VPN provider.
If I do a fresh os install and change vpn password will everything be ok?
A fresh OS install will likely get rid of the attacker from your specific system. It will not make it impossible for the attacker to use the already stolen credentials though. A password change might be sufficient but it might be that the attacker has added himself as recovery contact to the account. Or the attacker was the one who changed the password first and also the contact email and locked you out this way from your own account.