Python DataFrame Is there a way to make a new DataFrame only for the area you want?

Hello, I'm a beginner studying Python DataFrame.

I was dealing with DataFrame, and I didn't know anything about it, so I tried googling, but I couldn't find it, so I'm asking you a question.

I want to read the first df in Excel and make a new DataFrame that meets certain conditions in the value, but it didn't work well, so I'm asking you a question. For example, if I print only the area I want, it comes out as below. If you look at the row number below, it's 14, 15, 16, but I'm going to go back to 0, 1, 2, 3, 4... I want to make it a new DataFrame that starts with . I think it's simple, but I don't know the keyword and it doesn't come out well even if I search this and that.ㅠ<

// If you put the conditions you want in df, it comes out like this.
df_2=df_1.iloc[cnt1:cnt1+cnt2, :]
print(df_2)

    a1  Unnamed: 1  Unnamed:2   idx3

14  a2  0          0        ex2.x.8

15  p   p1        p2        ex2.x.9

16  q   q1        q2        ex1.x.5

// I want DataFrame to come out like this.
    a1  Unnamed: 1  Unnamed:2   idx3

1   a2  0          0        ex2.x.8

2   p   p1        p2        ex2.x.9

3   q   q1        q2        ex1.x.5