No way to retrieve it once you change it. I have a doc file on my main computer on;ly accesable from my admin accout that contains modem settings just in case.
You will need to do a factory reset of the modem.
Usually best to contact your ISP for specific instructions if you got the modem from them and let them walk you through it.
You will need to contact them anyway to get your Userer ID and Password unless you have it writtedn down some where.
Most modems will have a wizard to walk you through the setup when you connect it and you will only need to enter your DSL Username and password
This usually works with CenturyLink (Qwest) and AT&T DSL
Select autoconnect
Enter User Name and password when prompted.
Select Auto DHCP for WAN connection
Selet auto DNS server selection
If you need to do a manual setup.
Select Connection Type PPPoE
Enter DSL Username and password
Select Obtain IP Address and DNS information Automatically
Change MTU = 1500
VPI = 0
VCI = 32
General information you need for a DSL connection.
Type of connection
DSL User Name
DSL Password
Most telcos (AT&T, CenturyLink) are using autoconnect with auto DHCP and autoDNS.