Not sure what you did wrong so to fix it you just need to return to the "scene of the crime" so to speak.  Switch to the FORMS mode and click on the incorrect amount on the form it wound up on to data source where to make the correction.

A solo  401K contribution for a Sch C business is entered here :

If you are self-employed, you can enter your retirement contributions using these steps:

1. Click FEDERAL (Business in the Home & Business version)  > Continue > I'll choose what I work on
2. On the screen, Let's gather your business info, scroll down to the Less Common Business Situations section.
3. Click on the Start/Update box next to Self-Employed Retirement. 
4. On the Self-Employed Retirement Plans screen, click Yes.

The incorrect IRA contribution section is here :  

https://ttlc.intuit.com/turbotax-support/en-us/help-article/retirement-benefits/enter-traditional-ro...