How can I export Task.std file created using Task app on Samsung S2 to Samsung S6 Edge+?

[AC Question]

I have used Task App that came on Samsung S2 for about 4 years and I have about 400 task that I would like to keep for record. I backed up all data on S2 and managed to successfully restore it to S6 Edge+ except the Tasks did not appear on S Planner. I have to mention that I used to enter the tasks on Task app manually (i.e., Locally) and not through any other calendar like google. Please note that file extension is *.std.
I have spent hours and hours lately trying to solve the problem. I also could not find a way how to convert *.std file into iCalendar file presuming that I can import iCalendar file through S Planner.
Appreciate your help.
Khader