it really shouldn't be that hard, just find two corners and gently twist them together. tie it tight and double check that you didn't leave any gaps. if there's grounds, you can always filter them out.

Something I do is that I pour the beans into a cube then grind them back into the original bag to make the grounds easier to pour into the filter, also when pouring the water wait a few minutes before tying the filter for the water to be soaked up by the grounds it usually makes it easier to tie like that :)

May be tying the bag too tight and causing a rip?

I like to pinch the a corner of the bag and softly fold it about 1 inch or less in and out and and continue to do so until I get to the other end of the circle. I try not to force it to come together or else the bag rips. Once I tie it securely, I go back in and tie it around on more time. As for the water, I slowly pour it in by the sides. Hopefully this makes sense. I used to rip cold brew bags everyday when I started but now I make cold brew everyday as an opener. Hope this somewhat helps!

Also another thing is that if you leave the cold brew toddy under the grinder to catch the grounds, the pressure of the grinder rips the edge of the bag or grounds could end up on the outside of the toddy.