Potential consequences of providing voluntary work for a team I've been forced to leave I have been forced to leave my previous institute by my former principal investigator. 

At the institute I have solved problems regarding the software, and I enjoyed giving help as much as I can to many users, even after resignation. I had a request from users to do a tutorial video. 

I was thinking of that before resignation, but I am afraid that could be not favourable by the ex-PI. Although, a week ago I have received a message from him apologizing for what he did and wishing me good luck. Despite his behaviour, I forgive him. 

I would really like to do that video voluntarily, but I am not belonging to the institute anymore and I would like to keep things good and not fabricating sensitivity. Should I ignore the request of those potential users or do those tutorials on my own?
Personally, I think you should focus that time and effort into getting another position, if you have not got one already.

If you have a new position already, well done, then focus that time and effort into where you are now. They, hopefully, will appreciate that effort and motivation.