Please clarify whether you have a Roth account in the 401k, or a true Roth IRA. It is most common for an employer to have a 401k, which can have both traditional (pre-tax) and Roth (after tax) options. Funds are held at an institution chosen by the employer.
There is a provision in one of the SECURE acts that creates a new simple option called a payroll deduction IRA, where the employee sets up a personal IRA account at a bank or broker, and the employer makes an after-tax payroll deduction and sends it to the IRA on behalf of the employer. It would be unusual for an employer to offer both a 401k and a payroll deduction IRA.
https://www.irs.gov/retirement-plans/plan-sponsor/payroll-deduction-ira
An IRA (traditional or Roth) is not the same as a 401k (pretax or Roth) and the rules and contribution limits are very different.
If you only made contributions to the employer's plan, then everything you need to know will be on your W-2. Just enter the W-2 as-is. Don't enter any IRA contributions because you didn't make any.
If you set up your own IRA and made after-tax contributions via a "payroll deduction IRA", then the contributions won't be on your W-2 and you report them yourself.
