In both of the T20Is matches Muhammad Rizwan was not the part of the team and Muhammad Rizwan gave chance to Omair Yousuf. In the first match, he has not made too good but valuable effort as well. He scored 18 and lost his wicket but yesterday he was playing fast from the start and scored 22 while using 15 balls, he could score more but the target was chased that is why he remains not out.
I think today again Muhammad Rizwan would not be the part of the team and if Pakistan won the toss then they should try to back their batsmen because bowlers are in good form already but they have to make sure that there is backup of any batsmen in case the upper order don’t perform well.
In recent T20I matches as you said Muhammad Rizwan did not play so Omair Yousuf got chance to show what he can do. In first match Yousuf performance was okay he scored 18 runs before getting out but in second match he played much better. He started playing aggressively from the beginning scored 22 runs in 15 balls and did not get out because Pakistan reached the target they were chasing. Since Rizwan is still not playing Pakistan plan for next match should be to help their batsmen especially if they win the toss. Their bowlers are already playing well, but it's very important to have a backup plan in case the main batsmen don't play well.