How to change tile layer legend in arcgis online?

[FieldMapper]

Hi, 

I have what should be a really easy to solve problem, so I'm not sure if I'm missing something really simple! I want to change this layer so that it says Peat depth (cm) NOT Peat depth (m). In arcgis pro that's easy, and it's also very simple for feature class layers in online by configuring the popup. 

But for a tile layer in online I can't seem to figure it out! I've tried opening in pro, but can't edit since it's a tile layer. 

If anyone has any ideas to help, it would be much appreciated! 

[GormanJoe]

Have you found a solution to this? I'm having the same issue, but all I can think is to edit in ArcPro and overwrite the web layer.