Even though I hand sew almost every day, I do not use many different hand-sewing techniques every day. This morning I am sewing a rolled hem to finish a ruffle on a Lunardi hat for 1780s. Rolled hems are particularly helpful in sewing cap ruffles and other millinery projects, so I use this technique several times a year, but for some reason I forget how to get a perfectly formed rolled hem between the projects I use it on. There are several channels on YouTube I like to visit to brush up on hand sewing techniques.
Sewn Company by Sarah Woodyard has great videos on hand stitching and also offers classes. Sarah is not only an accomplished historical seamstress, but a delightful individual. I was honored to work with her at an event last August hosted by the Heritage Sewing and Skill Building Group in Savage, Maryland. The group offers classes and workshops on sewing from the colonial through the federal periods. They are now offering virtual programs as well.
Another place I like to look for hand-stitching technique videos is Burnley and Trowbridge. Most historic seamstresses and tailors know them for their beautiful historic fabrics and tools, but they also have a YouTube channel. Their page is filled with all types of videos to help you with your hand sewing and they have had classes and sew alongs this summer as well.