How do I file?

If you and your spouse live apart for at least the last six months of 2024, you will be able to file as Head of Household and claim your child as your qualifying dependent.  Your spouse will have to file as married filing separately.

Am I Head of Household?

https://ttlc.intuit.com/questions/1894553-do-i-qualify-for-head-of-household

https://ttlc.intuit.com/questions/2900097-what-is-a-qualifying-person-for-head-of-household

If you qualify as Head of Household, when you enter your marital status (single or married filing separately) into MyInfo, and then enter your qualifying dependent, TurboTax will offer HOH as your filing status.

The question, not addressed by the other answer, is does your child qualify.  You only said previous relationship.

The child qualifies you to file HOH if the child is:

1. Your biological child

2. Your stepchild (even if you divorced, the child still qualifies you)

3. Placed in your home by the state or a state-approved foster care agency.

4. Your adopted child.

However, if the child is not one of these types of relationships, and you just ended up caring for them because families are messy sometimes (for example, the biological child of a former partner whom you never married), they are not a qualifying child for HOH.

You weren't specific, so I just wanted to put that out there.  

If you and your spouse live apart for at least the last six months of 2024, you will be able to file as Head of Household and claim your child as your qualifying dependent.  Your spouse will have to file as married filing separately.

Am I Head of Household?

https://ttlc.intuit.com/questions/1894553-do-i-qualify-for-head-of-household

https://ttlc.intuit.com/questions/2900097-what-is-a-qualifying-person-for-head-of-household

If you qualify as Head of Household, when you enter your marital status (single or married filing separately) into MyInfo, and then enter your qualifying dependent, TurboTax will offer HOH as your filing status.