What's the rule for only haveing 3 qualifiers from one sub district, and having placed up to 6 at the other sub district. i.e

North Sub District 1 has only 3 qualifiers for 8 and Under 58lbs, and South Sub District 1 placed 6 at the tournament.

Does the 5th place qaulifier in South Sub District move into the 4th spot from the North Sub District?

It is up to each district to determine the manner in which wrestlers may advance from subdistrict to district competition. Section V (State Qualifying Folkstyle Tournament Rules) of the Kids Standing Rules states as follows:

this was done from north to south in 8u 88. the south had 3 and the north is sending 5 to district. You need to verify that but I think that is the case. I hope this helps.