Im not sure where you exactly want to add it. But you can use the formula DATEADD(date, 28, ‘days’) to calculate this date from another Thursday. (the is in case you have another date in another field that is actually a 2nd Thursday of the month).
If for example you want to add this in one field without another field having the date, you can do the following:
Create a field and call it sequence, make it as Autonumber.
Use this formula
DATEADD(DATETIME_PARSE("12 Mar 2020", 'D MMM YYYY'), sequence*28, 'days')