Hello
It would be really helpful to know what you are making, is there a designer or pattern name or number?
From the information you’ve given I would expect you to already have 56 stitches on your needle, is this the case?
Then on the next row cast on an additional 40 before working the row,. A knit cast on will work for this, you will have 96 stitches, work across this row with whatever the stitch pattern is.
Then, turn as though to begin the next row but before knitting cast on an additional 40 stitches at the beginning of the row. Now 136 stitches, work across these with the stitch pattern.
2 rows completed and 40 stitches cast on at the beginning of each row.
If you don’t have 56 stitches already then ignore this answer!
But someone can certainly help with a little more information.