Replace xx with next number in sequence

[fltsim.xx]
title=C172R Skyhawk Aviation PXI
sim=C172
model=
panel=
sound=
texture=SkyhawkPXI
kb_checklists=C172_check
kb_reference=C172_ref
atc_id=ZS-PXI
ui_manufacturer=A2A Cessna
ui_type="C172R Skyhawk"
ui_variation="Skyhawk Aviation (ZS-PXI)"
ui_typerole="Single Engine Prop"
ui_createdby="A2A Simulations Inc."
description="Skyhawk Aviation repaint by Calvin Diogo/CharlieDelta Textures"

[fltsim.xx]
title=C172R Skyhawk Aviation PXH
sim=C172
model=
panel=
sound=
texture=SkyhawkPXH
kb_checklists=C172_check
kb_reference=C172_ref
atc_id=ZS-PXH
ui_manufacturer=A2A Cessna
ui_type="C172R Skyhawk"
ui_variation="Skyhawk Aviation (ZS-PXH)"
ui_typerole="Single Engine Prop"
ui_createdby="A2A Simulations Inc."
description="Skyhawk Aviation repaint by Calvin Diogo/CharlieDelta Textures"