Officially? Just build more smelters. Note that, unlike some stuff, smelters will play "catch up" when you get near them again, effectively working while you are away.

Unofficially? Mods exist for pulling items from nearby chests. I think Valheim plus will do it, along with a bunch of other things. There might be a separate mod that specifically deals with smelters/crafting from chests, but I'm not aware of it. Obligatory disclaimer: mods are not supported by the devs at this time, and they take no responsibility for any mod-related issues that appear. If/when such issues do appear, remember to mention all mods used when asking for help/reporting it.