app.py

import gradio as gr

def change_tab(id):
    return gr.Tabs(selected=id)

with gr.Blocks() as demo:
    with gr.Tabs() as tabs:
        with gr.TabItem("Train", id=0): #index is 0
            t = gr.Textbox()
        with gr.TabItem("Inference", id=1): #index is 1
            i = gr.Image()
    
    btn = gr.Button()
    # When the button is clicked, switch to Tab1 (index 1)
    btn.click(change_tab, gr.Number(1, visible=False), tabs)
            
demo.launch()