How to change rootfs size and have two partitions

How can I change the rootfs (APP) size ?
And how to have two rootfs partitions ?

I tried changing settings in

For example APPSIZE
and adding
with no success.

Moreover what is the value of APPSIZE and where does it come from?

<partition name="APP" type="data">
    <allocation_policy> sequential </allocation_policy>
    <filesystem_type> basic </filesystem_type>
    <size> APPSIZE </size>
    <file_system_attribute> 0 </file_system_attribute>
    <allocation_attribute> 0x8 </allocation_attribute>
    <align_boundary> 4096 </align_boundary>
    <percent_reserved> 0 </percent_reserved>
    <unique_guid> APPUUID </unique_guid>
    <filename> APPFILE </filename>
    <description> **Required.** Contains the rootfs. This partition must be defined after
      `primary_gpt` so it can be accessed as the fixed known special device
      `/dev/mmcblk0p1`. </description>


Have you get some answers about your question please?
I have the same problem and would like create specific partitions .

Thanks for you answer