how to split forward and reverse reads from sam file

Hello everyone,

I have question please

I have bam file containing unmapped reads that I want to assemble.

I tried samtools fastq to obtain the two files forward and reverse

I did this command

samtools fastq -1 wPru_1_Unmapped_reads.fastq -2 wPru_2_Unmapped_reads.fastq   wPru_Unmapped_reads.bam

but when I wanted to perform the assembly (shovill) it didn't work it shows that the number of forward is larger than the number of reverse reads

The number of left read-pairs is larger than the number of right read-pairs

my objective now is how to extract forward and reverse reads from bam file

Thank you very much