I received a form 1099-K. I'm low-income and senior started a small business and sold $605.00 total in 2023. Do I need to file this and how do I find how much I owe ?

It depends. If expenses reduces the self employment income to less than $400 you will not be required to file. When income of $400 net earnings or more is received as an independent business owner a return must be filed,  If you had any expenses then you can use them to offset the income.  If your expenses bring the net income below $400 then self employment tax would not be required. Based on your total income there is no personal income tax. 

• How do I report income from self employment?

You also must file a federal return if: Filing Requirements

• You had $400 or more in self-employment net earnings (gross income minus expenses)