Well, you can limit the number of rows that can de added in ACF settings, but that doesn’t affect already added fields.
There must be a code snippet to do that for you, but I didn’t find it.
With CSS, you can set display to none from nth child of the repeater. You just have to target it right. But that does not seem the right thing to do.
:nth-of-type(1n+2){ display: none; }
You can create a new CPT instead of ACF repeater too.
Or maybe do it with a code block.