​@Stephaniew is this an image included in an email template?  there is 2 ways of going about it, there is the conventional way of implementing it as HTML image block and specifying the style to make it have rounded edges.  Alternatively you could leverage AI and ask Remix to do it for you.  Described in detail here

In addition to using the Remix tool that ​@whereisjad mentioned, the Klaviyo template editor also has a lightweight cropping of the images if that’s all you need.