@Paul421
This is a sole proprietorship so, from a tax perspective, there is no difference between you as an individual and the sole proprietorship. It would be redundant to sell your items to the business since the income and expense cancel each other out. It's like writing a check to yourself.
You can put them into inventory by assigning the opening balance of the item(s) to an owner's capital equity account. If you don't have an owner's capital account, set one up. As far as assigning a value to the items, if you recall what you paid for them, use that. If not, use the fair market value (FMV) of the items. Research the items online and keep some records to substantiate the FMV.
Or, you can assign the values to an expense account when you sell the items and not keep an inventory.