uncircumcised penis & oral.

So the first time I had a penis in my mouth it was a reasonable size and it was circumcised. I was able to please my partner to a point where he would even brag about it. Now with my second boyfriend it is totally different. His penis is really Big and it's not circumcised so I'm having trouble when it comes to having oral sex with him. I feel like I'm not doing a good job at all and it's super frustrating.  Do you guys have tips 👀