There're some videos doing this however its older versions and some nodes don't even exist anymore. Blur is gone and so subtract.
I have no idea how to blur my hdri.
Even tried photoshop but when i put it to blender theres a black line between the 0 and 360 angle
Not an answer to your question directly but will solve your problem. In Photoshop duplicate your unblurred HDRI to another layer so that it is on bottom. use Filter/Offset to offset image 50%. Blur both layers. Offset the offsetted layer back where it was, and erase the sharp borders from the original top layer. Voilà.
