First knitted garment...need guidance on assembling

I’m working on, and almost finished with, my first garment…Bernat’s Baby Jacquards Garter Stitch Kimono. (It’s a free pattern on the Bernat website but for some reason I can’t put a link to it in my post.) The pattern doesn’t provide detailed instructions for assembling the sweater and I’ve never assembled anything knitted before. I’ve made a lot of crocheted baby clothes that required assembling but it’s very different. I’ve looked in the video section but I’m still unsure about which method to use for this specific pattern. Any suggestions?

You can use mattress stitch to sew them all together. Start with the shoulder seams, then you can fit the top of the sleeves into them. I like to sew the sides and sleeve seams all in one seam.