Question Help with htaccess redirect

[Shaneee]

Hello. So I've changed my forum software and I've kept a copy of the old version which is still accessible by directing to the folder and the new version is on the subdomain.
How can I redirect old links for the subdomain that were linking to a viewtopic.php file to the direct folder now?

For example forum.example.co.uk/viewtopic.php?f=4 would need to redirect as example.co.uk/forum/viewtopic.php?f=4

The new forum uses index.php to link topics/forums so a wildcard redirect on viewtopic.php would be ideal.

Thanks.