Simple posted a few videos about Mylar blankets and uses. One was a video for bags for sealing long term storage (LTS) of food. It showed them using an iron, that you would use to iron clothes.
Hint: A hair straightener is much much easier. If you don't want to use your fancy one (it doesn't harm it if you do) pick up a cheap one. After sealing 100's of bags, I can tell you from personal experience this is so easy.
Just fill up your Mylar bag, drop in an oxygen absorber, and slide the flat iron across the top. Done.
To practice if you want to experiment try this:
Get a Capri Sun juice pouch. You don't need to rinse out for this. Cut off the top just below where the straw hole is. Make sure after you do this to look inside and cut again if you still see a little of the plastic strip inside. Now fill will water about half way, run the hair straightener across the top to seal and then squeeze the pouch. You should have no leaks. If there is seal again. The seal should be about 1/4" to 1/2" wide. It was that simple.
I like to keep the seal as small as possible, so that when I open the bag, most of the bag is still intact and you can clean and let dry and yes, reuse the bag again.
When you have food in the bag, you will know you have a good seal, because the O2 absorber will turn it into a brick. It should not have air in it after 30 minutes or so. If it does and this is for LTS, please reopen a corner, drop in another O2 absorber and re-seal.
Hope that helps someone. God Bless