A bit ago I trued my wheels up but in the process took a bit too much tension out.
My question is, If I true them up again, then add say half a turn of tension on each then re-check it will there be any problems or do I need someone with a proper tension gauge?

Just winch them all in by the same amount and you’ll be fine. Don’t forget to stress relieve the wheel before doing a final truing.

pick a pitch and tension to it.

Loose spokes break

Tight ones don’t, apparently.

Make sure any twist on the spokes is relieved occasionally through the process by putting the hub on the floor and pressing the rim on opposite sides, rotate and repeat for the other side. Hear them click straight when doing it.

Spokes twisted too much also snap.

Spokes should be as tight as possbut one side will usually be tighter than the other due to the dish.

The wheelpro pdf book is your bible. It’s money well spent. (£10 IIRC).

Work round from the valve and miss out every other spoke, thus tensioning one side first and then move onto the other. Quarter turn on each spoke at a time.