Wikidata administrators can create it for you.

Thanks @matej_suchanek. I will contact the administrators to create a tag for us.

Once the tag is created how can i add this tag while making wikidata edits. The mobile edits tags are being added automatically for us and the wbcreateclaims method of wikidata API doesn’t seem to have any parameter for adding tags.

Indeed, it does not (T155109). But you can make it in two steps: first create the claim and then add the tag via action=tag&revid={data.pageinfo.lastrevid} (with "data" being JSON of the response).

Thanks a lot @matej_suchanek! This is precious information for us. :)

@matej_suchanek I was trying to add this tag but I get the following exception:

{
    "error": {
        "code": "tags-apply-not-allowed-one",
        "info": "The tag \"'wikimedia-commons-app'\" is not allowed to be manually applied.",
        "*": "See https://www.wikidata.org/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce> for notice of API deprecations and breaking changes."
    },
    "servedby": "mw1221"
}

Does this API require any special permissions? The Android app would be making this call on behalf of the logged in user. What would be the best way to go ahead if this permission can't be provided to all users.

Per https://www.wikidata.org/wiki/Special:ListGroupRights#user, every logged in user should be able to apply a change tag. You have already managed to do so.

By the way, since change tags can be applied by any user, they can also become subject of vandalism. Rarely some users apply them manually to arbitrary revisions (but it isn't problem for anyone to revert it). So you may want to use reason= parameter to confirm it's a valid addition.