You can't. The only move tutor who teaches Seismic Toss is in FireRed and LeafGreen. Unless you had it there, then migrated it all the way up, your charizard can't learn it. But it shouldn't learn it, Charizard has better moves like Air Slash and Flamethrower. Teach it those. Not having Seismic Toss is not a loss to Charizard. Charizard is actually not that good with his Stealth Rock weakness though.
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dude! you need to trade!
You can't. Trade or link
Any Pokemon that can breed can breed with a ditto.