Adding in a new ball of yarn of the same colour

So I’ve been knitting a scarf in this pattern:
cast on 27 stitches

Row 1 (and only row) : slip first stitch purlwise, k1, p1 k2, p1 across

I want to add in a new ball of yarn, but all the videos I’ve seen on doing this show it done on a knit stitch and at the very start of the row. I can’t start at the very start though because of the slipped stitch, so where should I start it?

Also, I am a bit confused on the whole matter of adding in a new ball in the first place… I’m not sure of where to place the new working yarn, the new working yarn tail, and the old piece of working yarn no longer being used.

Help please! I would love to finally finish my scarf!

Anytime you have to add a ball of yarn you can just start knitting with it. It will leave a loose area, but you can loosely tie the ends together and then untie them and weave the ends in when you’re all done (or after a few rows if you want to. So slip your stitch and knit a few then add the new ball.

This reply may be too late but here is a video showing another way… there is also one on there showing joining 2 different colors.