I always liked this post from 2020 from an active member.
You could do a factory restore of Spark in dji assistant after syncing your flightlogs in GO4 app. Do not worry about the logs, they are synced to your dji account and your flying device (phone/pad)
New owner will need to create a new personal dji account or log in via his/her existing account.
Copy SD files and format card.
Clean all with a soft cloth.. done.
It seems simple enough.
Hope your son in law enjoys flying the SPARK.