you need to install the seqretbut that's a not so easy task you need conda etc.

what is more problematic, though, is that the GFF conversion via seqret is not that great either, I forgot the exact details, but there are inconsistencies

it is best if you get the gff directly; you could use a tool I wrote bio

pip install bio --upgrade

then you can do:

bio fetch AF086833 --format gff > AF086833.gff

or

 cat AF086833.gb  | bio gff > AF086833.gff

the two GFF files will not be identical, as the first obtains the GFF file from NCBI whereas the latter converts the GenBank to GFF.

The GFF distributed by NCBI may contain information that is not present in the GenBank file