Simple logic to see what is needed is to create a manual pirep or check an acars pirep directly from the database, then you can prepare your old data to match the new fields and import via some sql queries. Or of course you can write a custom module, utilizing laravel features to make it more complex if you wish.
Most important things is the data units, flight (pirep) times are in minutes and all weight / fuel values are in pounds (lbs) for phpvms v7 database (regardless what you select for display).
Also you may need to match your old pilot id's in those pireps with new user_id's you have in your system (don't mix them up with idents, I am talking about the real database indexed id numbers of users)
Then you may need to match your old airline codes with your new airline_id's to have more matches / reflecting details.
You can probably use the same timestamps for created_at, submitted_at, updated_at fields of v7, it will not harm the system but if you have detailed times you can use them too (created_at is the time a flight is started, submitted_at is the the it gets filed etc.)
Pirep type (manual/acars), pirep state, pirep status can be same for all these imported all pireps.
In theory if you can match the pilot id's with their old pireps, nightly cron can re-calculate their pirep counts and times according to that data (pilots will be happy).
What you will lose is financial details of those pireps (can be done if you want to go that deep but I think this is not important compared to the pirep itself), and detailed acars data (like logs, flown points etc) you may have in that old system.
Good luck