Sender IDs are only supported in certain countries, please refer to our documentation  to verify that you can register a sender ID for the country(ies) that you wish to send SMSs to.
The sender ID requests are handled by a different team. Please contact them by following the steps below :
1) Sign in to the AWS Management Console, and go to the AWS Support Center: https://console.aws.amazon.com/support/home#/
2) Choose "Create case".
3) Under "Create case", choose "Service limit increase".
4) Under "Case classification", do the following:
a) For Limit type, choose "Pinpoint SMS". Please note that, although you are choosing Pinpoint, it also applies to SNS.
b) For "Link to site or app which will be sending SMS", identify the website or application where your audience members opt in to receive your SMS messages.
c) For "Type of messages", choose the type of message that you plan to send using your sender ID.
d) For "Targeted Countries", specify the countries where you want to register a sender ID. Support for sender IDs and sender ID registration requirements vary by country.
5) Under "Requests", do the following:
a) For "Resource Type", choose "General Limits".
b) For "Limit", choose "SenderID Registration".
c) For "New limit value", type the number of sender IDs that you're requesting. Typically, this value is "1".
6) Under "Case description", for Use case description, provide the following information:
a) The sender ID that you want to register.
b) The template that you plan to use for your SMS messages.
c) The number of messages that you plan to send to each recipient per month.
d) Information about how your customers opt in to receiving messages from you.
e) The name of your company or organization.
f) The address that's associated with your company or organization.
g) The country where your company or organization is based.
h) A phone number for your company or organization.
i) The URL of the website for your company or organization.
See this links, might help.