How do I increase and decrease the volume from the earbuds?

Based on the user manual for the acer OHR640 True Wireless Earbuds, there are no specific touch commands listed for adjusting the volume directly on the earbuds themselves.

The manual provides the following instructions for the multifunction touch keys:

• Playback/Pause: Press the left or right earbud once.
• Previous Track: Press the left earbud twice in succession.
• Next Track: Press the right earbud twice in succession.
• Noise Cancellation Mode: Long press the left or right earbud for 1 second.

To adjust the volume, you must use the volume controls on your connected device (smartphone, tablet, or computer). The manual specifically advises in the safety guidelines to adjust the sound on your device to an appropriate level to avoid hearing damage.