How can I make the tires on a wheeled walker not slide (even though tire locked and not moving)?

Willie, I now understand.

I was reading this as the rollator is skidding even though the brakes are engaged, which is definitely possible with some wheels on a smooth floor.

Here is a video.

https://www.google.com/search?q=how+to+keep+wheels+on+rollators+not+slide&client=ms-android-samsung&source=android-home&sxsrf=AJOqlzVJX7uxDQInLRmvVWYrfqdVJGUvrA%3A1677806481254&source=hp&ei=kUsBZIy0C7XZ5NoPp9GlqAU&oq=&gs_lcp=ChFtb2JpbGUtZ3dzLXdpei1ocBABGAAyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwguEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECcyBwgjEOoCECdQAFgAYO4ZaAFwAHgAgAEAiAEAkgEAmAEAsAEP&sclient=mobile-gws-wiz-hp#

There is a video, second one down that illustrates how the brake works.

Not all people should use Rollators because they can get away from them. They have to have the strength to squeeze the brake.

Is it a regular metal frame walker or the rollator kind?

You may be able to find replacement anti slip wheels, or it may be easier or more economical to shop for a different rollator with rubberized anti slip wheels built in.

Call the manufacturer to see if they have any solutions.