ensure the latest tranlog backup you managed to copy over to the secondary server is restored to the secondary database. Easiest way is to see what the latest file is in the directory you are copying to and check in errorlog to see if that has been restored

Bring the database online with command

restore database yourdatabase with recovery

You may need to sysnch orphaned userids (only applicable if using SQL authentication)

in your database run

sp_change_users_login 'report'

if any rows returned run

sp_change_users_login 'update_one','loginname','userid' --check that order don't have BOL here

for each orphaned id.

The need to do this can be avoided by using sp_help_revlogin to copy logins over.

The application will also need to be repointed, easiest way to do this is a DNS alias.

If log shipping is failing usually one of the SQLAgent jobs involved will be failing (they all start LS) or warnings will be appearing in the errorlog of the secondary that logshipping is out of synch