You simply have to include wording in your will and a donation/bequest. This donation can be financial or asset based (property etc). The following paragraph is a suggestion to updating your will :
“I leave $(Amount) to Animal Rescue Support Incorporated ABN 25 151 709 481 for its general purposes and I direct that the receipt of the secretary, treasurer, or other proper officer of that organization is a sufficient receipt for my Trustee and that my Trustee is not obliged to see to the application of this bequest.”
The above wording will need to be adapted for your particular circumstances. For example you may wish to leave a percentage of your assets to the Craft Guild (Animal Rescue Support Incorporated) rather than a lump sum, or perhaps a particular valuable asset, such as shares, an antique, or real estate.