Other than a lot of lube, I'd say maybe try warming up with smaller toys first...like smallest toy, then a slightly bigger toy, then an even bigger one, etc. until you can get that one in without much or any pain.
I know that usually helps me when I want to use a bigger toy than usual, even if it does mean it takes a bit longer.

Thank you so much! What should be the duration of that process?

Well if you have a lot of time to spare and won't get bored, you could probably take a few hours to warm up and then use that toy. Once your body is used to the size though, it probably won't be much of an issue. If the product page is accurate, a 1 1/2" diameter isn't all that hard to work up to.
...actually it might even be more the shape than the size itself that's the issue, it's more rounded than tapered so I'd expect it to be a bit more difficult to insert if you're not used to that size toy.

There's also this item that might help as well.

What exactly is the issue? Is it the girth? Is it that when you insert the arm doesn't match up? Message me with the details and I'll help you out. If this toy doesn't work for you...then I can help you find one that will.