In order to call a block method from a Magento 1 template, you will first need to get an instance of the block object. This can be done using the following code:
$block = Mage::app()->getLayout()->createBlock('block_name');
Once you have an instance of the block object, you can then call any public methods on it. For example, if the block has a public method called sayHello(), you can call it like this:
$block->sayHello();