You don't need a 1099-MISC to report your self-employment income. You can report it based on your own records of how much you received. You don't have to provide any documentation with your original tax return or amended tax return. Just enter the amount of income. If the IRS wants documentation of the income they will send you a letter later. You should have been keeping a record of your income from the side job (as well as any related expenses). If you do have a record, that's the only documentation you need. If you don't have a record, reconstruct the amount of income based on bank deposits or whatever other information you have available. If necessary, estimate the amount the best you can from memory. If you are still doing the side job, start keeping records now for 2019 and later.
