Use the Brand Mentions filter (Content Filter section). Enter the brand's account name — the @ is optional — and influData finds creators whose posts mention that account, e.g. creators who tagged @zara in their content. This is the standard way to find out which creators already work with a competitor or have mentioned your own brand organically.
If you enter several brands, creators must have mentioned all of them (AND), which is useful for finding creators active in a specific brand set. Prefix a brand with - to exclude creators who mentioned it. The search covers the posts indexed in influData's content database; use the Content Timeframe filter to limit it to mentions within the last 7 to 365 days.