The best pH value for carrots should be neutral, in the range of 6.5 to 7.5. There are potatoes that do well in neutral soils and if youâÂÂre trying to knock the pH down from 7 to 5 or so, some selective potato shopping might help the years go by faster!

You could add âÂÂacidicâ things such as peat or sulphur but confronted with the scale of all that groundsâ mineral mass verses a little old humanâÂÂs measuring cup, itâÂÂs like spitting in the ocean and watching it rise. Sulphur needs time and microbes to become effective. I donâÂÂt use it on food, but I hear that too much all at once can be bad for things actively growing right there.

Fresher manure tends to be acidic to neutral, especially if wet with urine, but some stables are known to add lime for odor control so results may be all over the map. For true acid-demanding plants, have you considered containers to cut down on the amount of soil you have to manipulate?

I stole this from gardengal48 and it makes sense to me:

Soil pH is dependent primarily on the underlying mineral content of the soil and the amount of rainfall. Soils with a mineral base composed of mostly igneous rock, as do those with higher rainfalls, tend towards an acidic pH. Areas with more sedimentary rocks like limestone or sandstone tend towards a more alkaline pH.

The use of synthetic fertilizers can alter pH to some degree, usually more acidic, but the effect tends to be temporary as soils will tend to return to their natural pH. Accumulation of plant debris may have an impact on the pH at the soil surface but will have no significant change on the chemistry of the underlying soil.

7 is close enough ... carrots are pickier about soil texture than pH. So are potatos

What, or who, did that soil test for pH? The home garden soil test kits, or testers, are not very reliable although a soil pH "around 7" is good enough for most all plants. While most all sources will tell you that the "best" soil pH for growing carrots is 6.0 to 6.8 that is also the range for most all plants. That range is also the range most all soil nutrients are most readily available to plants, but 7.0 is not all that far out of range.
What ever you do to change that soil pH will take much longer then it would take to grow the carrots. The best time to test soil is in the fall so you do have time to make the necessary changes. Testing just before the growing season is not a real good time, although better then not testing.