Discuss the process with your printer before you start. I am not sure if silk screen is 4 colour or Pantone, but my expectation is 4 colour, in which the normal process is as follows:
Ideally for commercial printing you need a profile of the output process, if not you need a CMYK description, such as FOGRA 39 CMYK.
Get that off the printer then Image > Edit > Convert to Profile and select the appropriate CMYK description / profile from the list.
If you then convert the file again to sRGB you can print it via a lab and get a reasonably accurate proof.
Garment steamers are not a "new" invention. Do they work? On some items yes (sweaters) but on most items of clothing, to get the proper finish it requires heat, pressure and steam. Steam is not always the best for all types of garments. Take dress shirts for example. Without heat and pressure and not a lot of steam, you end up with a limp wrinkled shirt. Suit coats and pants require pressure and heat also. Do not pay too much attention to the infomercials on TV. A trained eye sees that the items they "steam to perfection" are brand new and just barely wrinkled. They are not (the clothes) like clothing that just came out of the washer and dryer or that were hung to dry.