I have some bed sheets which got a yellowish taint, so I used bleach to brighten it, and now I have some bleach stains and it's still a bit yellowish.

This was obviously a failure, but the fabric itself is still OK, so to cover the taint and the stains up I would like to dye it dark.

Can you tell me any place which does offers a dyeing service in Chiang Mai?

If none of these exists, recommendations on where to buy dye are also welcome, somehow if I search for "fabric dye" on Lazada nearly nothing shows up.

Dyes are readily available in a multitude of colors at any sewing notions shops.  "Goon" is located just outside Warorot Market.  There's another shop across the street from Goon.

 

https://goo.gl/maps/LBqKASqhyQDyYW1r5

 

Here's a shop that dyes clothing for you:  ย้อมผ้า /yawm pa/ means dye cloth.  I know that they dye the dark blue shirts that traditional farmers wear.  Be cautious of the bleeding of the dye onto other articles of clothing during the first few washings, however.  The colors are not colorfast, and they continue to wash out in the laundry.

 

https://goo.gl/maps/7TLBWdxdpkTjJC1V7

i take stuff to this shop in the small alley behind Miguel's restaurant. 
httpins://maps.app.goo.gl/6rqVcwJz6A3FWz147

At the intersection, they have an incorrectly spelled sign that says "Dying -->"

10 hours ago, captainjackS said:

i take stuff to this shop in the small alley behind Miguel's restaurant. 
httpins://maps.app.goo.gl/6rqVcwJz6A3FWz147

At the intersection, they have an incorrectly spelled sign that says "Dying -->"

That is the very same place that I suggested in the post above yours.