How to clean a canvas print?

[combat squirrel]

As title I have a dark dirt mark on a large A0 canvas along the top where it was stacked wrong - but it's a very light colour (whitey blue sky), i tried very gently on a v small bit with a semi damp cloth and its not really done much and left a stain where the water was, any ideas on how to clean it and not affect the print ?

 

[testbloke]

Most canvas prints normally have either a laminate or varnish making it really easy to clean. If this is bare canvas you are going to struggle. Try a pencil eraser

 

[combat squirrel]

Damn thats a shame, appears to be just bare canvas

 

[Tradecanvasprint]

Most canvas prints normally have either a laminate or varnish making it really easy to clean. If this is bare canvas you are going to struggle. Try a pencil eraser

My thoughts exactly...... I'd even think about simply leaving it as more cleaning attempts may make it even worse.