How do I change from single to head of household in previous years

[DoninGA]

You have to have a qualifying person as a dependent to be eligible for Head of Household.  If you do not have a dependent you will remain Single.

See this TurboTax support FAQ for head of household - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-filing-status/qualify-head-household...

See this TurboTax support FAQ for amending a prior year tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...