If you put the items required to craft, lets say a diamond pickaxe in a crafting table, then fill your inventory, then shift click on the diamond pickaxe that appears in the crafting table, it will get the rarity of it.
You can reroll that by taking out then putting back in one of the crafting ingredients and shift cliking it again, until you get a good rarity, like seen in the video below.

https://github.com/Draylar/tiered/assets/162575964/32ddf1ad-c6bf-422d-94b3-6d16509c4250
.