I have created a volume that is 10 GB. so now I want to merge this 10GB volume to my root volume. my root volume size is 25 GB so the storage accessible under root / how can I do that?

root@test:~# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            481M     0  481M   0% /dev
tmpfs            99M  592K   98M   1% /run
/dev/vda1        25G  989M   24G   5% /
tmpfs           493M     0  493M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           493M     0  493M   0% /sys/fs/cgroup
/dev/vda15      105M  3.6M  101M   4% /boot/efi
/dev/sda        9.8G   37M  9.3G   1% /mnt/volume_blr1_02
tmpfs            99M     0   99M   0% /run/user/0

As you can see the additional storage volume is added as separate mount point as:

/dev/sda 9.8G 37M 9.3G 1% /mnt/volume_blr1_02

What I want is, total 35GB storage accessible under root / how can I do that?