Adding yarn

I have started a pattern and you knit with 2 stands of yarn on the 4th row you knit with a differnt yarn and then on the 5th you go back to the 2 stands of yarn. You repeat this pattern. My question How do I add the extra yarn and then go back to the original two.

You would just start knitting with the new yarn, and if you only knit one row with it, then you’re going to have to cut the 2 strands so you can knit with them on the other edge. Make sure you leave the tails long enough to weave in when you’re done.