musical meter with a denominator 7/8

Hello. As announced in 5.4 release notes I have a corrupted session with a 7/8 meter. How do I proceed to correct this.

Thanks for helping. Best regards

There is a session utility called ardour5-fix_bbtppq which is likely to be supplied by your linux distribution.
It can also be built from source by specifying the dummy backend during waf configuration.
Running the utility with -h or with no arguments will print some usage information which is worth reading.
If you have problems getting your hands on this, please contact me via mainsbridge at gmail dot com.