I'm knitting a pullover in the round. To make armholes, I put stitches for FRONT on a holder and I have knit the BACK flat decreasing as required.
Those BACK stitches on a holder now.
How do I get yarn from the finished BACK to the FRONT in order to knit FRONT flat decreasing as required?
Break the yarn leaving a fairly long tail for finishing.
Rejoin the yarn to the front and continue knitting flat.