Hi,
Here’s the [http://h10032.www1.hp.com/ctg/Manual/c06172053|maintenance and service guide] for the laptop, taken from this [https://support.hp.com/us-en/product/hp-envy-15m-bq100-x360-convertible-pc/16851057/model/18967057/manuals|webpage]
Go to p.31 to view the necessary pre-requiste steps and then the procedure to remove the battery.
Also on p.31 you will find the part number for the battery. Search online for ''HP 916814-855'' to find suppliers that suit you.