VCF to plink format wrong variant id

Question

[ete]

Hi,

I converted my VCF file into plink binary formats by using plink2. As variant ID I need the following format (chrom_pos):

          chrom   snp         cm        pos   a0  a1      i
0          0      Chr1_657   0.0        657   T   C       0
1          0      Chr5_1168  0.0        1168  G   T       1

But I get only a point (.)

       chrom  snp   cm     pos     a0 a1   i
 0     7H      .    0.0    176267  G  C   0
 1     7H      .    0.0    176270  A  G   1
 2     7H      .    0.0    176273  G  C   2

How to achieve this?

Thanks