Unfortunately this can’t be done automatically.
In principle, you control the line appearance with the Entries
Structure & Formatting descriptors. But, the caption is collected as a whole without being decomposed into “label”, figure number and caption proper. This means you can’t insert “decorations” like tab characters between those.
The only thing you can do is to increase the left indent in Figure Index 1 paragraph style but not knowing where the caption will effectively begin (and it varies from one entry to the next because the figure number changes) will not set the indent relative to the beginning of the caption.