Yes I would like to know how do I file for my third stimulus 2021 do I need to fill out a form because they have no taxes for that year

You can file a 2021 tax return and use the recovery rebate credit in Federal Review to seek the 3rd EIP payment that went out for 2021.   If someone could claim you as a dependent for 2021, you were not eligible then and will not be eligible now.   Before you file a return, make sure you did not receive it already.   Check your online account with the IRS to see what they show for you.

If you did not receive the 3rd stimulus check, you can get it by filing a 2021 tax return and use the recovery rebate credit in Federal Review.    The stimulus amount will show up on line 30 of the Form 1040.

Check your own bank account for deposits of the stimulus checks, and check your online account with the IRS to see what the IRS shows they sent to you.

Try checking your online account with the IRS (and if you filed a joint return—check for BOTH of you)

https://www.irs.gov/payments/your-online-account

If you need to trace a payment that the IRS says has been issued to you, mail or fax a completed IRS Form 3911,

Taxpayer Statement Regarding Refund.

Online preparation and e-filing for 2021, 2022, and  2023 is permanently closed.

Note:  The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac.  It cannot be used on a mobile device.

To file a return for a prior tax year

 If you need to prepare a return for 2021, 2022, or 2023  you can purchase and download desktop software to do it, then print, sign,  and mail the return(s)

https://turbotax.intuit.com/personal-taxes/past-years-products/

You may also want to explore purchasing the software from various retailers such as Amazon, Costco, Best Buy, Walmart, Sam’s, etc.

Remember to prepare your state return as well—if you live in a state that has a state income tax.

https://ttlc.intuit.com/community/state-taxes/help/how-do-i-contact-my-state-department-of-revenue/00/25573 

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as certified mail so you will know the IRS/state received the return.

Federal and state returns must be in separate envelopes and they are mailed to different addresses.  Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.

Or use the paper forms to mail:

Here is the IRS 2021 Form 1040
https://www.irs.gov/pub/irs-prior/f1040--2021.pdf

or if you want bigger type use 1040SR for Seniors,
https://www.irs.gov/pub/irs-prior/f1040s--2021.pdf

And 2021 Instructions
https://www.irs.gov/pub/irs-prior/i1040gi--2021.pdf

2021 Tax and EIC Tables
https://www.irs.gov/pub/irs-prior/i1040tt--2021.pdf

Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2021.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2021.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2021.pdf