The u-boot side should be around here (Android 9):
u-boot/include/environment/ti/boot.h

It will look something like this:
Note that the a and b are only if you have a/b updates enabled. If you do not, you will not see a and b.
#define PARTS_DEFAULT \
	"uuid_disk=${uuid_gpt_disk};" \
	"name=xloader,start=128K,size=128K,uuid=${uuid_gpt_xloader};" \
	"name=bootloader,size=768K,uuid=${uuid_gpt_bootloader};" \
	"name=reserved,size=384K,uuid=${uuid_gpt_reserved};" \
	"name=misc,size=128K,uuid=${uuid_gpt_misc};" \
	"name=efs,size=16M,uuid=${uuid_gpt_efs};" \
	"name=crypto,size=16K,uuid=${uuid_gpt_crypto};" \
	"name=boot_a,size=16M,uuid=${uuid_gpt_boot_a};" \
	"name=boot_b,size=16M,uuid=${uuid_gpt_boot_b};" \
	"name=dtb_a,size=256K,uuid=${uuid_gpt_dtb_a};" \
	"name=dtb_b,size=256K,uuid=${uuid_gpt_dtb_b};" \
	"name=system_a,size=4G,uuid=${uuid_gpt_system_a};" \
	"name=system_b,size=4G,uuid=${uuid_gpt_system_b};" \
	"name=vendor_a,size=100M,uuid=${uuid_gpt_vendor_a};" \
	"name=vendor_b,size=100M,uuid=${uuid_gpt_vendor_b};" \
	"name=ipu1,size=1M,uuid=${uuid_gpt_ipu1};" \
	"name=ipu2,size=1M,uuid=${uuid_gpt_ipu2};" \
	"name=userdata,size=-,uuid=${uuid_gpt_userdata}"
?


It also needs to be changed on the Android side on the BoardConfig.mk file for the appropriate board. 
aosp/device/ti/beagle_x15/BoardConfig.mk

It will look something like this:
BOARD_SYSTEMIMAGE_PARTITION_SIZE := 2147483648 # it is in bits 

You will need to tell Android what your interface name is:
location of the config.xml file that you need to update with the interface name for Android. 
aosp/device/ti/beagle_x15/overlay/frameworks/base/core/res/res/values/config.xml

something like this:
<string-array translatable="false" name="config_tether_wifi_regexs">
        <item>"mlan\\d"</item>
</string-array>