When you have two such pages with similarities but different purpose, you can usually find different keywords for the two pages. Your second step is trying to narrow down the type of t-shirt, so I'd recommend finding a more specific phrase. Maybe one of:
- Regular t-shirt
- Men's t-shirt
- Unisex t-shirt
- Crew neck t-shirt
I'm also not sure why you are using the word "design" in two of the four links. "Design" could apply to all four of those links. Rather than use it in the anchor text of each of them, you should use it in a question or heading. I'd think it would be clearer if you phrased it as:
What type of t-shirt would you like to design?
- Men's t-shirt
- Woman's t-shirt
- Oversize t-shirt
- Child's t-shirt
That way, the first page of your flow would be targeted at "Design t-shirt" and the second page of you flow would be targeted at the more specific "Men's t-shirt."
For what it is worth, Yoast is being overly pedantic. The anchor text that you use internally on your site to your own pages doesn't make much of a difference for SEO these days. Eight years ago Google gave a lot more weight to it. That rule in Yoast is likely left over from the days when that anchor text could have mattered.
It is a useful exercise to think carefully about each page's keyword targeting, but it isn't an "SEO error" to use the same anchor text internally point to two different pages. I'd fix this on your site mostly because I think it would be confusing for users to have to click on "Design t-shirt" twice to get to the correct type of shirt they want.