It’s possible to take a bus/drive from Dake Onsen up to hachigome (8th stage). From there it’s a short hike up to the top. Alternatively Lonely Planet recommends a tough hike up from Iwakisan Jinja
岩木山神社
大字百沢字寺沢27 弘前市 青森県
The hike is a steep 1400m climb over 6km followed by a long long descent to Dake onsen if you don’t use the bus