First Step is to identify the cause of gap whether genetic or local factors are involved.
Second is the treatment planning in which the options usually are
1) Orthodontic correction wires and braces
2)Composite buildup or Veneers
3) Capping on teeth
The best treatment options are judged out by a dentist.
My recommendation for you would be to consult an aesthetic Dentist for the same.
There are many ways to close gaps in teeth. Depending on your condition and age.
1. Orthodontic Treatment (braces)- with this your teeth are aligned with the help of wires & brackets. Teeth positioned in their respective positions thus closing the gap.
Now a days clear aligners or invisible braces are also available.
2. Composite bonding- it is the cheapest way to close the gap. But the two teeth are increased in size.
3. Porcelain Veneer & Crowns- These are more durable than bonding.