I am trying to solve this problem but i cannot figure out how to fix this?Can you please help me?

My code so far:

```
for _ in range(int(input())):
n = int(input())
s = input()
m = 'abacaba'
k = 0
li = []
for x in range(len(m)):
if m[x] == s[x] or s[x] == '?':
li.append(m[x])
else:
li.append(s[x])
# i don't know, am i in the right way to solve this
```

I try this in codeforces.Here is the original link of this problem.