Hello,
Could you provide URL of the mentioned product?
As I can see you already wrote styles for heading – https://prnt.sc/1vesfq9
If you want to change it globally, use the next custom CSS code:
.tab-description h1 {
font-size: 20px;
}
.tab-description h2 {
font-size: 19px;
}
.tab-description h3 {
font-size: 18px;
}
Regards