YO, put hook into ch ( or st if it's a later row) , pull yarn through, yo pull through 2 loops and STOP.
Do NOT complete that treble, insteadv do YO and repeat the process making a second part-completed treble.
Now below is showing you the two part completed treble stitches and now it's yarn over (YO) and through all the 3 loops on the hook that you can see here
Then we work 2 Tr in this stitch and 2TR in the next stitch: you can see this below:
I have drawn a diagram of this but cannot locate my phone charger lead right now to transfer the photos of the diagram so that will be edited in later.